Harnessing Z-scheme charge transfer in ultrathin C3N5/TiO2@Ti3C2Cl2 MXene nanosheets for sustainable water purification, hydrogen evolution, and biocompatibility

MXenes have recently emerged as one of the most promising conductive supports for photocatalytic water remediation and hydrogen evolution reaction (HER) electrocatalysts. This study presented the synthesis of a novel nanocomposite, TiO₂@Ti₃C₂Cl₂, using a one-step molten salt-shielded (MS³) method under an air atmosphere at a low temperature of 1000 °C. A unique aspect of this process was the successful extraction of copper from molten salt using iron bars without any chemical agents. The synthesized TiO₂@Ti₃C₂Cl₂ was subsequently coupled with low band-gap carbon nitride (C₃N₅) via an ultrasonic (US) technique, forming a Z-scheme ternary (C₃N₅/TiO₂@Ti₃C₂Cl₂) nanocomposites with a 2D/0D/2D structure. The ternary nanocomposite exhibited remarkable photocatalytic performance, achieving 100% efficiency in degrading dye molecules under optimal conditions, which included a pH of 5, a nanophotocatalyst dose of 100 ppm, a rhodamine B (Rh B) concentration of 10 ppm, room temperature, and a reaction time of 30 min. The C₃N₅/TiO₂@Ti₃C₂Cl₂/Cu composite also exhibited promising electrocatalytic performance for HER with a Tafel slope of 103 mV.dec⁻¹ and an overpotential of 51 mV at a current density of 10 mA cm⁻² under alkaline conditions. The significant improvement in photocatalytic water remediation and HER performance is likely due to several key factors: the strong interfacial coupling between the 2D/0D/2D materials, which promotes efficient charge separation; the reduced recombination rate of electron-hole pairs, enhancing photocatalytic efficiency; the highly improved electron-transfer processes, which accelerate reaction kinetics; and the increased number of exposed photo- and electrocatalytic active sites, providing more surface area for reactions. These combined effects result in better overall performance for photocatalytic and HER applications. Furthermore, the MTT assay demonstrated a reduction in the toxicity of C₃N₅ upon forming the ternary nanocomposite. These findings suggest that the synthesized ternary nanocomposite enhances photocatalytic and HER efficiency and reduces toxicity, making it a valuable material for environmental and energy applications.